Dehydrogenation of alkyl aromatic compounds in the presence of nickelbearing alloy steels



N. B. KING Oct. 28. 1969 DEHYDROGENATION 0F ALKYL AROMATIC COMPOUNDS INTHE PRESENCE OF NICKEL-BEARING ALLOY STEELS 14, 1967 2 Sheets-Sheet 1Filed Dec.

- NORMA/V 8. KING INVENTOR.

FIG. I.

ATTORNEYS Oct. 28. 1969 N KING 3,475,508

B. DEHYDROGENATION OF ALKYL AROMATIG COMPOUNDS IN THE PRESENCE OFNICKEL-BEARING ALLOY STEELS Filed Dec. 14, 1967 2 Sheets-Sheet 2 34 A Ta ETHY LB ENZEN E STEAM- FIG. 2.

NORMAN B. Kl/VG INVENTOR.

ATTORNEYS United States Patent 3,475,508 DEHYDROGENATION OF ALKYLAROMATIC COMPOUNDS IN THE PRESENCE OF NICKEL- BEARING ALLOY STEELSNorman B. King, Wayland, Mass., assignor, by mesne assignments, to TheBadger Company, Inc., Cambridge, Mass, a corporation of Delaware FiledDec. 14, 1967, Ser. No. 690,650 Int. Cl. C07c /18, /10

US. Cl. 260669 19 Claims ABSTRACT OF THE DISCLOSURE Dehydrogenation ofalkyl aromatic compounds involving reactors constructed in part ofnickel-bearing alloy steels and in part of nickel-free alloy steels.

The present invention relates to dehydrogenation of alkyl aromatichydrocarbons and more particularly to the conversion of ethylbenzene tostyrene.

Styrene is a well known commercially available material having a widevariety of uses, including manufacture of polystyrene plastics,styrene-butadiene latex and other polymer products. It is most commonlymade by catalytically dehydrogenating ethylbenzene. As conventionallypracticed liquid ethylbenzene feed is vaporized, superheated, and passedtogether with superheated steam through a dehydrogenation reactorcontaining a bed of suitable catalyst. This dehydrogenation reaction ishighly endothermic and the considerable drop in temperature whichaccompanies the reaction has the effect of limiting the yield. Yieldrefers to the ratio of moles of styrene appearing in the product,multiplied by 100, to the moles of ethylbenzene entering the reactor. Tooffset the aforesaid temperature drop and thereby achieve a suitableyield, sufficient heat is supplied directly or indirectly to thereactants or the dehydrogenation equipment to maintain the temperatureof the mixture in the region of 550 to 660 C.

Heretofore it has been the practice to construct the dehydrogenationreactors of alloy steels having substantially little or no nickelcontent. This practice has been predicated on the ground that thepresence of nickel promotes cracking of the hydrocarbon feed toundesirable products and results in carbon formation, reduced styreneyield, catalyst deactivation, and possible plugging of the catalystsystem. However, the use of non-nickel alloy steels has resulted in moreexpensive dehydrogenation equipment because the allowable designstresses for such steels are relatively low at the high temperaturesinvolved in the process. In particular the pressure-containing shells ofthe reactors require large design thicknesses which, coupled with thepoor mechanical properties of nickel-free alloy steels, makesfabrication difficult and greatly increases equipment cost. A furtherproblem with non-nickel containing alloy steels is thatthey tend toundergo metallurgical changes when subjected to substantial temperaturechanges, e.g., when the equipment is cooled down.

The general object of the invention is to provide a substantialimprovement in the art of dehydrogenating alkyl aromatic hydrocarbons.

A further object of this invention is to provide a new method andapparatus for the dehydrogenation of alkyl aromatic hydrocarbons such asethylbenzene whereby the foregoing disadvantages are overcome.

A more specific object of the invention is to provide new and improvedreactors for dehydrogenating alkylated aromatic hydrocarbons, notablyethylbenzene, that are characterized by high through-put at relativelylow pressure drops, even distribution of reactants, high yields, greaterstrength, relatively little or no metallurgical deformation resultingfrom substantial changes in temperature, and lower cost of construction.

According to this invention, dehydrogenation is effected in one or morereaction zones each comprising a reactor designed so that all but aselected section thereof in which the initial reaction occurs is made ofnickel bearing alloy steels. This selected initial reaction section isfabricated 0f non-nickel bearing steels. The use of low allowable stressnon-nickel bearing steels in the initial reaction section is feasiblesince it is not a pressure-containing part of the reaction vessel. Thisdesign is predicated on the discovery that cracking into undesired sideproducts, substantial carbon formation and other harmful effects on thedehydrogenation system will occur only if the hot unreacted alkylaromatic compounds contact nickel bearing steels while unmixed withsteam or only partially mixed with steam. More specifically this designis derived from the discovery that the usual harmful effects are avoidedif contact with the nickel bearing steels occurs after the alkylaromatic feed and steam have been mixed and the dehydrogenation reactionhas started and proceeded sufliciently to release hydrogen gas as one ofthe reaction products.

The foregoing objects and advantages are better appreciated and theinvention better understood by the specific details presented belowwhich are to be considered together with the accompanying drawing,wherein:

FIG. 1 is a sectional view of a preferred form of a reactor constructedin accordance with the invention; and

FIG. 2 is a schematic flow diagram of one illustrated embodiment of thenovel process.

Turning now to FIG. 1, the reactor comprises a cylindrical outerpressure shell 2 fabricated of a suitable nickel-bearing alloy steel,e.g., series 300 austenitic stainless steels. The bottom head 4 of shell2 is provided with an opening in which is mounted an inlet pipe 6 madeof a non-nickel alloy steel, e.g., a series 400 stainless steel. Theinner end of pipe 6 is closed off by an end head 8 which also is made ofthe same non-nickel stainless steel. That portion of pipe 6 locatedwithin shell 2 is provided with a multitude of holes 10 sized to permitoptimum flow of the fluid reactants which are supplied to the reactorvia conduits (not shown) connected to pipe 6.

The pipe 6 is surrounded by a concentrically disposed cylindrical wall12 which also is provided with a multitude of holes 14 sized to permitoptimum flow of reactants and reaction products. The bottom end of wall12 is secured to the bottom head 4 of shell 2. The upper end of wall 12is secured to a head plate 16. Head plate 16 which covers wall 12 isimperforate. Wall 12 and plate 16 both may be made of the samenickel-bearing alloy steel used to fabricate shell 2.

With this construction the wall 12, pipe 6, and that portion of bottomhead 4 extending between pipe 6 and wall 12 together form a. largevolume chamber that contains a bed of a suitable catalyst 24 in particleform. In this connection it is to be appreciated that the relative sizesof the catalyst particles and the holes in pipe 6 and wall 12 are suchthat the particles cannot pass through the holes; alternatively theholes 10 and 14 may be substantially larger than the catalyst particlesbut covered with a fine mesh screen having openings smaller than thecatalyst particles. The upper end head 26 of shell 2 has an outlet portfitted with a pipe 28 which serves to deliver the reactor efliuent toassociated process equipment, e.g., another reactor or a productrecovery stage.

It is to be appreciated that FIG. 1 is directed to the essential aspectsof the reactor design and that in practice the reactor may embodyvarious conventional features and details of construction. For example,the reactor may be fitted with one or more manholes permitting access toits interior for inspection and maintenance purposes. Thus, FIG. 1 showsthe upper end head 26 fitted with a manhole pipe 30 having a removablecover 32.

It :also is to be understood that any one or a combination of a numberof nickel-containing alloys and stainless steels may be used for thereactor walls and heads. By way of example, but not limitation; suchparts of the reactor may be made of one or more of the following: Type302, 304, 321 and 325 stainless steels. Similarly, the inlet pipe 6 maybe made of any one of a variety of non-nickel alloy steels.

With a reactor designed generally as illustrated in FIG. 1 and as abovedescribed, all reactant feed mixing is completed and initial reactionoccurs in the internal central pipe 6. Since this pipe is made ofnon-nickel steel, it is unaffected by the reactants and will produce noside cracking or other harmful effects on the dehydrogenation reactionif the steam and alkyl aromatic feed are not completely mixed as is truejust after the reactants are introduced thereto. The initialdehydrogenation reaction occurring in pipe 6 releases hydrogen gas asone of its products. The initial reaction products and the unreactedreactants produce no significant degree of cracking and little or nocarbon formation when brought into contact with the nickel-containingwall 12, plate 16, or shell 2.

Reference now is had to FIG. 2 which is a schematic flow diagram of oneillustrative embodiment of the novel process directed to conversion ofethylbenzene to styrene. This illustrative embodiment employs tworeactors A and B with the outlet pipe 28A of reactor A connected to theinlet pipe 6B of reactor B through a heat exchanger 34. The heatexchanger 34 and the inter-connecting pipes 28A and 6B may beconstructed of nickel containing alloy steels. Steam, preferablysuperheated, is introduced via a pipe 36 to the outer section of heatexchanger 34 and, after heat exchange with the eflluent of reactor A, itpasses via a conduit 38 to the inlet pipe 6A where it it mixed withethylbenzene feed supplied by a feed pipe 40. The final product mixleaves reactor B via its outlet pipe 28B and is introduced into aconventional product recovery system (not shown) where styrene isseparated from the other reaction products and recovered.

In this system of FIG. 2, the conversion of ethylbenzene to styrene iseffected in both reactors, with the effiuent from reactor A (comprisingstyrene, ethylbenzene and steam) being heated to a desirable temperatureby heat exchange with the steam supplied by pipe 36. This indirectheating is simple and offers the advantage that the same steam used toheat the efiiuent of reactor A is that employed in the dehydrogenationreaction.

The quantity of steam fed to reactor A depends upon the particularalkylated aromatic hydrocarbon making up the feed stock. In the case ofethylbenzene, conversion to styrene with a yield of 50-60% requiresabout 10-20 moles of steam per mole of ethylbenzene. The operatingtemperatures are not narrowly critical but can vary over :a moderaterange. Thus, the ethylbenzene-steam mixture fed to reactor A may bewithin the range of 580 C. to 660 C. while the efliuent from reactor Ahas a temperature of about 550-610 C. In passing through exchanger 34the effluent from reactor A may be reheated to the identical temperatureas the reactant mixture delivered by inlet pipe 6A or to a higher orlower temperature. Preferably the entering temperature of thehydrocarbonsteam mixture fed to reactor B is about the same as that forreactor A.

Substantially any well-known dehydrogenation catalyst may be used fordehydrogenation of alkyl aromatic hydrocarbons according to thisinvention. These include ferric oxide-potassium oxide, magnesiumoxide-ferrous oxide-potassium carbonate, and alumina-silica-nickelcatalysts. These catalysts are arranged in beds having a height to depthratio (the depth is measured from the central pipe 6 to the cylindricalwall 12) ranging from about 5:1 to about 40:1,- with the preferred ratiobeing about 10: 1.

The following example serves to illustrate the preferred mode ofproducing styrene from ethylbenbene according to this invention.

EXAMPLE Two reactors designed as described above are coupled together inthe manner illustrated in FIG. 2. Each reactor has a catalyst bed with aheight to depth ratio of about 10:1. The catalyst is a promoted ironoxide type having an average particle size of inch. Ethylbenzene andsteam are delivered to reactor A at the relative rates of 72.6 and 220pounds per hour respectively. The ethylbenzene delivered via pipe 40 hasa temperature of about 550 C. while the steam fed via pipe 36 has a.temperature of about 682.5 C. The steam-ethylbenzene mixture has atemperature of about 642 C. as it enters reactor A. The efiiuentwithdrawn from reactor A has a temperature of about 595 C., but due toreheating in exchanger 34, it has a temperature of about 640 C. when itenters reactor B. The efiiuent from the second reactor is withdrawn at atemperature of about 617.5 C. This efiluent is then fed to aconventional recovery system where styrene is recovered.

In this two stage system, the ethylbenzene feed is partiallydehydrogenated to styrene upon contact with the fixed catalyst .bed inreactor A and additional dehydrogenation occurs when the effluent fromreactor A passes through the catalyst bed in reactor B. The overallconversion to styrene i.e., the ratio, multiplied by 100, of the molesof ethylbenzene converted to styrene in both reactors to the moles ofethylbenzene fed to reactor A, is in excess of 50%.

It is to be appreciated that this invention is not limited to styrenebut embraces the dehydrogenation of other alkylated aromatichydrocarbons such as isopropylbenzene, diethylbenzene, etc. to producedifferent vinyl substituted aromatic hydrocarbons. Furthermore thenumber of reactors that may be employed is variable and more than tworeactors may be employed in a system provided provision is made forheating between stages. Where more than two reactors are used thetemperature of the steam initially introduced into the system isadjusted to provide the desired degree of temperature rise for theefiiuent passing from one reactor to another. As a practical matter, thetotal number of reactors is determined by the economy of the process.

With reactors designed as herein described, the hydrocarbon and thesteam may be premixed before introduction to the pipe 6 of reactor A ormay be mixed Within the pipe as in the preferred embodiment. If thesteam and hydrocarbon are premixed before delivery to pipe 6, then theentire reactor A including pipe 6 may be made of nickel bearingstainless steel. However, this alternative procedure is less desirablesince it produces a somewhat smaller yield. It is believed obvious that,in either case, the subsequent stage reactors, e.g. reactor B, may bemade wholly of nickel bearing steels. It also is contemplated that theflow of gases through the reactors may be reversed. More specifically,it is contemplated that the hydrocarbon and steam may be premixed andthen fed through pipe 28 into the space surrounding the catalyst bed,passed through the catalyst bed, and then withdrawn through pipe 6. Thismode of operation is feasible and will not result in substantial carbonformation or undesired side products due to cracking since it ispredicated on the hydrocarbon and steam being fully premixed beforecoming into contact with the nickel-bearing steels of the reactor. It isto be understood also that reactor may be designed so that the inletpipe 6 is at the top and the outlet 28 is at the bottom, in which casethe system shown in FIG. 2 would be modified to provide for downwardrather than upward flow of reactants and reaction products.

A dehydrogenation reactor designed as herein described and illustratedoffers several advantages. For one thing it is a radial flow systemofiering high through-put with a relatively low pressure drop (about/2-1 pound per square inch per reactor) 'between the internal pipe 6 andthe outer shell 2. Hence the inner pipe 6 is not a pressure containingmember and the stresses to which it is subjected are well within theallowable limits for non-nickel austenitic stainless steels. On theother hand, the higher allowable stress limits and greater ductility ofthe nickel bearing steels used to fabricate the shell and interior wall12 make possible larger diameter equipment and greater flexibility indetails of design (with consequent capital cost savings) than arepossible if nickel-free alloy steels are used for the same parts.

As used herein the terms nickel-free alloy steel and non-nickel alloysteels means alloy steels that are substantially free of nickel or havea nickel content no greater than 0.75%

Other modifications and variations of the process and apparatus hereindescribed will be apparent to persons skilled in the art. Therefore, theinvention should be considered as including all modifications,variations and alternative forms falling with the scope of the appendedclaims.

I claim:

1. In a process for dehydrogenation of an alkyl aromatic hydrocarbonfeed in the presence of steam which comprises passing a mixture of saidhydrocarbon and steam through a reactor having an outer shell formed ofa nickel-bearing alloy steel and a catalytic dehydrogenation zone withinsaid shell, the improvement which comprises mixing said hydrocarbon feedand steam in a chamber within said reactor constructed of a non-nickelalloy steel, dehydrogenating part of said hydrocarbon feed in saidchamber, and passing the resulting mixture of hydrocarbon feed, steam,and dehydrogenation products through said catalytic dehydrogenation zoneso as to further dehydrogenate said hydrocarbon feed.

2. The process of claim 1 wherein the effluent of said reactor is passedthrough a second reactor having a second catalytic dehydrogenation zoneso that the dehydrogenation of said feed is effected in both reactors.

3. The process of claim 1 wherein said hydrocarbon feed is essentiallyethylbenzene.

4. The process of claim 3 wherein -20 moles of steam are supplied foreach mole of ethylbenzene.

5. The process of claim 3 wherein the mixture of hydrocarbon feed andsteam is at a temperature in the range of 580-660" C. in said chamber.

6. The process of claim 2 wherein said hydrocarbon feed comprisesethylbenzene and said efiluent is heated to a temperature of about550-610 C. before it passes to said second reactor.

7. The process of claim -6 wehrein said effluent is heated by indirectexchange of heat from said steam.

8. A process for dehydrogenating an alkyl aromatic hydrocarbon whichcomprises the steps of pre-mixing said hydrocarbon with steam,introducing the mixture into one end of a nickel-bearing alloy steelreactor containing a bed of dehydrogenation catalyst disposed betweentwo concentric chambers, passing said mixture radilally through said bedfrom one chamber to the other, and removing the products of reaction andthe unreacted portion of said mixture from the opposite end of saidreactor.

9. A dehydrogenation reactor comprising a closed shell having an outletat on end, an inlet pipe extending into said shell from the end oppositesaid one end, and means in said shell defining a catalyticdehydrogenation zone surrounding said inlet pipe in the path ofreactants flowing from said inlet pipe to said outlet, said shell beingformed of high allowable stress steel and said pipe being formed of anon-nickel alloy steel.

10. Apparatus adapted for dehydrogenation of alkyl aromatic hydrocarbonscomprising a closed shell having an outlet at one end, an inlet pipeextending into said shell from the end opposite said one end, mechanicalmeans within said shell defining a chamber surrounding said pipe andcommunicating with said inlet pipe and said outlet, and adehydrogenation catalyst within said chamber, said shell and saidmechanical means being made of nickelbearing alloy steels and said"inlet pipe being made of a non-nickel alloy steel.

11. Apparatus as defined by claim 10 wherein said pipe is provided withorifices that permit radial flow of reactants through said chamber.

12. Apparatus as defined by claim 10 wherein the ratio between thelength of said chamber measured along the longitudinal axis of saidshell and the depth of said chamber measured radially from said inletpipe is in the range of5:1to40:1.

13. A system for dehydrogenating alkyl aromatic hydrocarbons comprisingtwo reactors as defined by claim 10, means for introducing a mixture ofsteam and an alkyl aromatic hydrocarbon to the inlet pipe of onereactor, and means connected between the outlet of said one reactor andthe inlet pipe of the other reactor for delivering the effluent fromsaid one reactor to the other reactor so that the alkyl aromatichydrocarbon undergoes dehydrogenation in both reactors.

14. A process for dehydrogenating an alkyl aromatic hydrocarboncomprising intimately mixing said hydrocarbon with steam and initiatingdehydrogenation of said hydrocarbon in a first chamber of a reactorwhere the hydrocarbon-contacting surfaces thereof are a non-nickel alloysteel, passing the mixture of hydrocarbon and steam and the products ofinitial dehydrogenation to a second chamber of said reactor whichcontains a dehydrogenation catalyst and where at least in part thehydrocarbon-contacting surfaces thereof are a nickelbearing alloy steel,further dehydrogenating said hydrocarbon in said second chamber underthe influence of said catalyst, and collecting the products of thedehydrogenation reaction from said second chamber.

15. The process of claim 14 wherein said non-nickel alloy steel is a 400series stainless steel and said nickelbearing steel is a 300 seriesstainless steel.

16. The process of claim 14 wherein said chambers are in concentricrelation to each other, and further wherein the How of hydrocarbon,steam and the products of initial dehydrogenation is substantially in aradial direction through said second chamber.

17. The process of claim 14 wherein said hydrocarbon and steam arepassed to said second chamber only after the initial dehydrogenationreaction has proceeded sufficiently to release hydrogen gas as one ofits products.

18. A process for dehydrogenating an alkyl aromatic hydrocarbon using areactor having a first chamber in which its hydrocarbon-contactingsurfaces are a nonnickel alloy steel and a second chamber in which itshydrocarbon-contacting surfaces at least in part are of a nickel-bearingalloy steel, said second chamber containing a dehydrogenation catalyst,comprising mixing said hydrocarbon and steam in said first chamber underconditions such that dehydrogenation of said hydrocarbon is initiated insaid first chamber, passing the resulting mixture of hydrocarbon, steamand initial dehydrogenation reaction products to said second chamberunder conditions such that further dehydrogenation of said hydrocarbonis catalyzed by said catalyst, and collecting the products of reactionfrom said second chamber.

19. In a method'of performing a high temperature dehydrogenationreaction wherein a hydrocarbon feed is subjected to a temperature atwhich formation of carbon is promoted if the hydrocarbon feed iscontacted with a nickel-containing alloy steel, the improvementcomprising supplying said hydrocarbon feed and steam to a reactor havingan outer pressure shell made of a nickel-bearing steel, mixing saidhydrocarbon feed with steam in a first chamber of said reactor in whichthe surfaces thereof exposed to said feed are made of a nonnickel alloysteel, said mixing being effected under conditions such that part ofsaid feed is dehydrogenated, passing the resulting mixture ofhydrocarbon feed, steam and dehydrogenation products from said chamberthrough a catalytic reaction zone in said reactor and furtherdehydrogenating said feed in said zone under the influence of saidcatalyst, and collecting the products of dehydrogenation from saidreactor.

References Cited UNITED STATES PATENTS DELBERT E. GANTZ, PrimaryExaminer 10 C. R. DAVIS, Assistant Examiner US. Cl. X.R.

